title: Low temperature incommensurately modulated and noncollinear spin structure in FeCr2S4.
abstract: FeCr(2)S(4) orders magnetically at T(N)≈ 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below ∼ 60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (μSR) spectroscopy was carried out between 5 and 200 K together with new (57)Fe Mössbauer measurements. Below ∼ 50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Néel transition is of second order, but ill defined, extending over a range of ∼ 10 K. The Mössbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.
authors.affiliation: Physics Department, Technical University Munich, D-85747 Garching, Germany. kalvius@ph.tum.de
authors.forename: G M
authors.initials: GM
authors.lastname: Kalvius
authors.forename: A
authors.initials: A
authors.lastname: Krimmel
authors.forename: O
authors.initials: O
authors.lastname: Hartmann
authors.forename: R
authors.initials: R
authors.lastname: Wäppling
authors.forename: F E
authors.initials: FE
authors.lastname: Wagner
authors.forename: F J
authors.initials: FJ
authors.lastname: Litterst
authors.forename: V
authors.initials: V
authors.lastname: Tsurkan
authors.forename: A
authors.initials: A
authors.lastname: Loidl